Effects of morphine on various measures of peripherally versus centrally induced pain in rats will be compared. The central structures to be stimulated include the nuclei: parafasicularis thalami, ventralis-thalami-pars dorsomedialis, gigantocellularis in reticular formation, nucleus of the spinal tract of the trigeminal nerve; the root of the trigeminal nerve, the spinothalamic tract. Various brain stimulation parameters will be tried. Escape learning will be used to validate nociceptive quality of brain stimulation. Hot plate, tail flick, and running-jumping will be used to index peripheral effects.